/Engine/Source/Editor/UnrealEd/Public/Toolkits/AssetEditorToolkit.h
Returns the default extensibility managers, these are applied for all asset types
static [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FExtensibilityManager](API\Editor\UnrealEd\Toolkits\FExtensibilityManager) > GetSharedMenuExtensibilityManager()